A bank quotes a spot rate that is verifiably incorrect and deviates substantially from the...

you should hit the price and hold the bank to the quoted incorrect rate, as the quoted party is entitled to hold the quoting party to an erroneous rate

you should ask the dealer to check his price, as it is highly unethical for one party to hold another to an erroneously agreed rate

you should point out the mistake and split the difference

you should keep on dealing with this bank until the mistake is rectified